The present invention relates to the field of catalyst supports, especially for use in catalytic converters for automobiles. The catalyst support of the present invention is of the type which is known as a "honeycomb", because the support has a cross-section which resembles a honeycomb. The terms "honeycomb" and "catalyst support" are used interchangeably herein.
Catalyst supports having a spiral shape have been known in the prior art. The spiral structure is simple to build, but it has suffered from a major disadvantage which has limited its use for catalytic converters. This disadvantage is that the spiral supports of the prior art telescope outwardly, due to the pulsating exhaust of the automobile.
In Paper No. 850131 of the Society of Automotive Engineers (SAE), the production of a metal catalyst support having a "racetrack" cross section is described. By "racetrack" is meant the shape which is obtained when a circle is divided along a diameter, and the resulting semicircles are separated by a distance of about one radius, the semicircles being connected by tangents. This shape is commonly used for catalytic converters for automobiles. In the cited SAE paper, a flat strip and a corrugated strip are wound together on a mandrel, and then the mandrel is removed. The catalyst support is flattened in a press to convert the cylindrical cross section into a racetrack. The round hole in the center becomes a straight line seam parallel to the flat sides of the racetrack.
So far, the only known way to prevent telescoping has been to braze together the layers of the spiral over a short length at each end of the spiral. For example, the cited SAE paper states that the layers of the catalyst support must be brazed to prevent the support from telescoping. While brazing does prevent telescoping, it is expensive, and it also restricts the choice of metal for the spiral to those metals that can be brazed. Such metals are not the best catalyst supports.
The present invention provides a structure which prevents telescoping of the layers of a spiral catalyst support. The invention does not require brazing of the metal, so that any metal can be used. The invention also includes a method of making a metal spiral-shaped catalyst support.